This invention relates to a reactive polymeric scavenger for the room temperature removal of water and oxidant impurities from hydride or inert gases and to a process for purifying hydride or inert gases. More particularly, this invention relates to a polymeric scavenger containing reactive heteroatom functionalities containing reactive metallic species for removing water, oxidant and other impurities from hydride or inert gases.
At the present time, numerous industries require the use of purified gases in their processes. Even ppm or ppb levels of contaminants can have deleterious effects on the appearance or performance of certain products. For example, the grain structure of deposited silicon films can be significantly degraded by elevated oxygen levels in the reactor. Because of this and other adverse effects, the purification of process and purge gases in the microelectronics industry has found widespread acceptance and usage. The two principal methodologies for the point-of-use (pou) purification of inert and hydride gases are the room temperature removal of the gas impurities with an organometallic species on a high surface area support and the elevated temperature reaction with a metal alloy getter. The ideal purification material removes the unwanted impurities without generating volatile by-products that would contaminant the gas. It would be advantageous to have a high surface area support or membrane that in itself is the reactive species rather than attempting to deposit an uniform layer of reactive species onto a support. The purification material and resulting by-products should not be volatile under vacuum or pressurized flow conditions. Ideally, the purification material would operate at room temperature and not require electrical power for operation.
U.S. Pat. Nos. 4,603,148 and 4,604,270 describe a scavenger for purifying inert fluids consisting of a macroreticular support containing numerous pendant metallated functional groups corresponding to the general formula: ##STR2## where Ar is an aromatic group radical containing one to three rings, R.sub.1 and R.sub.2 can be the same or different and can be hydrogen or an alkyl group of 1-12 carbon atoms, methylene-bridged benzophenone, fluorenone or alkali or alkaline earth salts of these radicals and M is a reactive metal, e.g., lithium, sodium, potassium, alkyl magnesium, or alkyl zinc. The excess organometallic reagent utilized to metallate the pendant organic groups of the polymer is located within the pores of the polymer. These excess metallating agents in this purification material will generate hydrocarbon impurities upon reaction with the water impurity in the gas to be purified. Although the excess metallating agents can be converted to metal hydrides through a thermal treatment, the resulting metal hydrides will liberate hydrogen upon water removal from the gas stream.
U.S. Pat. No. 4,659,552 describes a scavenger for purifying arsine and phosphine consisting of the product of the reaction of arsine or phosphine with a macroreticular support containing pendant functional groups having the formula: ##STR3## wherein Ar is an aromatic hydrocarbon having one to three rings, R.sub.1 and R.sub.2 can be the same or different and can be hydrogen or an alkyl group of 1-12 carbon atoms, and M is lithium, sodium, or potassium. Reactive organometallic species are located within these pores of the polymer. These scavengers have the same undesirable characteristics as do the scavengers described in U.S. Pat. Nos. 4,603,148 and 4,604,270.
U.S. Pat. No. 4,761,395 describes a scavenger for purifying arsine, phosphine, ammonia and inert gases that consists of an anion which is reactive to gaseous impurities that is non-covalently deposited onto a support. The anion is selected from carbanions whose corresponding protonated forms have pKa values of 22-36 and anions formed by the reaction of these carbanions with the primary component of the gas. Although this scavenger will not have a hydrocarbon emission problem as with the previously discussed purification materials, there is the potential for volatilization of the protonated carbanion under vacuum or pressurized flow conditions. It would be more advantageous to have the support material itself be the reactive species, since the vapor pressure would be much lower. In addition, there is the potential for loss of surface area or obstruction of pores from the deposition of the reactive carbanion onto the high surface area support.
Chichibabin, A. E.; Seide, O. J. Russ. Phys. Chem Soc., 1914, 46, 1216 originally discovered the conversion of pyridine to 2-aminopyridine using sodium amide via an intermediate metal derivative. It was later found that organolithium compounds (RLi) would undergo addition reactions to nitrogen containing heterocyclic aromatic compounds to produce the lithiated products as depicted below for the pyridine case: ##STR4##
These pyridyl intermediates have been isolated and characterized by Giam, C. S.; Stout; J. L. J. Chem. Soc., Chem. Commun. 1969, 142 and others. These intermediates have found some applications as reducing agents for ketones (Abramovitch, R. A.; Marsh, W. C.; Saha, J. G., Can. J. Chem. 1965, 43, 2631), and for the formation of substituted heterocycles via carboxylation of the intermediate with carbon dioxide (Doyle, P.; Yates, R. R. J. Tetrahedron Lett. 1970, 38, 3371).
It would be desirable to provide a composition suitable for purifying gases while avoiding the production of volatile by-products. Furthermore, it would be desirable to provide such a composition which is effective for use at a normal operating condition and room temperature.